1. Field of the Invention
The field of the invention is cooling systems of internal combustion engines, specifically those with reciprocating pistons. The invention provides consistent controllable temperatures for each of the cylinders in a multi-cylinder engine.
2. The Prior Art
Conventional systems for cooling cylinder heads provide coolant patterns which go generally from one end of the cylinder head and block to the other. The complicated coolant flow pattern that results is a combination of longitudinal flow and cross flow, but all cylinders are cooled together with a common coolant flow path.
The conventional approach is successful in that engines generally do not overheat. However, the temperatures may vary between cylinders in a way that some cylinders are cooled just barely enough, while other cylinders are overcooled. This difference in cooling can affect the distribution of fuel and air into the cylinders and the initiation of combustion, such that not all of the cylinders attain optimum performance due to cylinder-to-cylinder cooling differences.
Wilkinsonxe2x80x94U.S. Pat. No. 5,058,535 teaches the use of a common rail cooling system which directs coolant flow to individual cylinders of flat (180xc2x0 vee) aircraft engines.
Wellsxe2x80x94U.S. Pat. No. 4,601,265 disclose a common rail coolant routing system with an inlet common rail and an outlet common rail on the same side of the cylinder block of an in-line engine. The system of Wells is designed to deliver equal amounts of coolant to each cylinder.
Haugen et alxe2x80x94U.S. Pat. No. 6,279,516 disclose a coolant cross-flow coolant flow system which directs the coolant flow across the cylinder in two levels, essentially over, up, and out, and attempts to minimize any flows between adjacent cylinders.
Abe et alxe2x80x94U.S. Pat. No. 5,386,805 teach a system having a separate inlet and outlet rails for the coolant and also teaches the possibility of using a separate coolant flow pattern in the cylinder block (crossflow) which is different from the coolant flow pattern in the cylinder head.
Kasting et alxe2x80x94U.S. Pat. No. 4,284,037 disclose an engine coolant flow pattern which is substantially separate for each of the cylinders in a multi-cylinder engine. The approach of Kasting et al attempts to provide an equal flow to each cylinder by a static structural design.
Bartolazzixe2x80x94U.S. Pat. No. 5,975,031 teaches the use of a single temperature sensor in a feedback control system for the fuel pump output and/or the amount of coolant flow bypassed to the radiator.
Takahashi et alxe2x80x94U.S. Pat. No. 5,769,038 teach a design of the coolant flow pattern intended to deliver a uniform amount of coolant delivered to each combustion chamber cooling area, in an attempt to provide equal cooling to the cylinders, without active control of the coolant flow.
Iwamoto et alxe2x80x94U.S. Pat. No. 4,665,867 teach a design of the coolant flow passages on the inlet side of the coolant system that attempts to equalize the coolant flow to each cylinder of a multicylinder engine, without active control of the coolant flow to individual cylinders.
Nakanishi et alxe2x80x94U.S. Pat. No. 4,212,270 disclose the use of two cooling systems, one for the cylinder head and the other for the cylinder block of a multi-cylinder engine.
The present invention provides open-loop control of individual cylinder cooling with control of the coolant flow to each cylinder provided by multiple sensors (typically, one per cylinder) and individual cylinder coolant flow control valves. This active control of separate and different coolant flows is in contrast to static designs for coolant flow control as exemplified by the Wilkinson, Wells, Kasting, Takahashi and Iwamoto references mentioned above.
The system of the present invention is an individual cylinder coolant control system which includes an inlet common rail, an outlet common rail, a coolant temperature sensor, and a coolant control valve for each cylinder (fewer or more sensors and valves are also possible) and an optional bypass valve to control coolant flow to the inlet common rail. The inlet common rail and/or the outlet common rail can be an integral part of the cylinder head of the engine or be separate from it.
In the individual cylinder coolant control system of the present invention, the coolant flow is separate for each cylinder, each separate flow is actively controlled, the flow direction is across the cylinder head, and the temperature of each cylinder is individually controllable.
Accordingly, the present invention provides a cooling system for an engine including a cylinder block having multiple cylinders covered and closed by a cylinder head. The coolant system includes an inlet rail and an outlet rail located on opposing sides of the cylinder head and a pump for feeding coolant flow through a discharge line into the inlet rail. A return line serves to return coolant from the outlet rail to the other portions of the cooling system and subsequently back to the pump, a plurality of individual coolant flow passages extend within the cylinder head and connect the inlet rail with the outlet rail. A control valve and an associated temperature sensor are provided within each of the coolant flow passages and a controller individually controls each of the control valves in accordance with the signal received from its associated temperature sensor.
The present invention further provides a method for individually controlling the temperature of each of multiple cylinders within a cylinder block and covered by a cylinder head. The method involves passing coolant through separate coolant flow passages, across the cylinder head, between an outlet rail and an inlet rail, sensing the temperature within each of the coolant passages and adjusting and controlling flow through the coolant passage containing the temperature sensor, responsive to a signal from the temperature sensor, to bring the sensed temperature for each of the coolant flow passages into conformance with a predetermined optimum temperature. The method may further include sensing engine load and/or engine speed and determining an optimum temperature, as the predetermined temperature, in accordance with the sensed engine load and/or engine speed. The method may further include directing the flow of coolant from a pump to bypass the inlet and outlet rails and coolant flow passages, during warm-up of the engine, until a sensed temperature reaches a predetermined minimum value. The coolant flow passages may be entirely separate with one coolant flow passage provided for each of the cylinders.
Preferably, a coolant flow passage is uniquely associated with each of the cylinders and the controller, individually for each cylinder, controls a control valve to bring the temperature detected by the associated temperature sensor into conformance with a predetermined optimum temperature. The predetermined optimum temperature may be an optimum temperature for a given load and/or engine speed stored in a memory readable by the controller.
Each of the coolant flow passages may be split so as to pass on both of opposing sides of an exhaust valve, an inlet valve, and/or an ignition device.
The coolant system preferably further includes a bypass rail for connecting the discharge line to the return line, bypassing the inlet and outlet rails and the coolant flow passages, and a splitter valve for selectively directing the discharge of coolant from the pump to the inlet rail and/or to the bypass rail.
Preferably, the coolant system has the inlet and outlet rails formed within the cylinder head.
Accordingly, the present invention provides the following advantages over the prior art:
1. Independent control of the temperature of each cylinder of a multicylinder engine,
2. Rapid warm-up of the passenger compartment,
3. Improved cold-start and warmup efficiency,
4. Lower cold-start and warmup emissions, and
5. Improved warmed up efficiency.